This invention relates to thermosettable resin compositions. In one embodiment, the invention relates to enhancement of the processing properties of bismaleimides.
Advanced composites are high-performance materials made up of a fiber-reinforced thermoplastic or thermosettable material. Thermosettable materials useful in advanced composites applications must meet a set of demanding property requirements. For example, such materials optimally have good high-temperature properties such as high (above 200.degree. C.) cured glass transition temperature and good mechanical strength. For ease of processing in preparing prepregs for composite parts, the uncured material will ideally have a low (below 120.degree. C.) melting temperature and a wide temperature range of processable viscosity (a wide "processing window").
Bismaleimide resins have superior high-temperature properties but are very brittle and further tend, because of their high softening points, to require solvents in order to be readily processable. In addition, standard cured bismaleimide resins tend to have high (in the 5-7% range) 93.degree. C. water absorption. Addition of thermoplastic or cyanate-terminated oligomers to bismaleimides increases the toughness but produces uncured mixtures so high in viscosity that fiber impregnation and processing by standard thermoset techniques are difficult.
It is thus an object of the invention to provide new thermoset resin materials. In one aspect, it is an object of the invention to provide curable additives which reduce the melting and softening points of bismaleimides yet cure to high-Tg, tough resins.